Cathode ray tube and light beam control means



Dec. 12, 1944.

R. E. RICKETTS CATHODE-RAY TUBE AND LIGHT BEAM CONTROL MEANS Filed July24, 1942 505672 72 2 CZ/6 Z55 Patented Dec. 12, 1944 CATHODE RAY TUBEAND LIGHT BEAM CONTROL MEANS Robert Eugene Rlcketts, Plainfleld; N. J.

Application July 24, 1942, Serial No. 452,221

7 Claims.

source, a source of secondary emission electrons which are produced bythe'bombardment of an electron emitting element by the primary orinitially produced electrons and which are com densed with the primaryelectrons into the spot or trace producing ray which is directed againstthe fluorescent screen and is caused to move thereacross in thecustomary manner.

Still another object of the invention is to provide an improvedcathode-ray tube having. as the cathode for the production of theprimary electron streams, a light sensitive electron emitting screen orwall in an end of the tube which is activated by the application theretoof a pencil or beam of light.

Still another object of the invention is to provide an improvedcathode-ray tube having the light sensitive electron emitting screenforming the cathode, with a novel means for controlling or varying theintensity of a light beam applied thereto, in accordance with or inresponse to received signals or signal impulses, whereby to obtain thedesired variations in intensity of the electron beam falling upon thefluorescent screen within the tube.

Still another object of the invention is to provide in association withan improve cathoderay tube of the character stated, an improved lightbeam intensity controlling cell operating upon the principle of the wellknown Kerr cell, in response to variations in received signals.

The invention will be best understood from a consideration of thefollowing detailed description taken in connection with the accompanyingdrawing, it being understood. however, that the invention is not to beconsidered as limited by the specific illustration or description butthat such illustration and description constitute a preferred embodimentof the invention.

In the drawing:

Figure 1 is a view illustrating the light beam control means, and aportion of the tube.

Figure l is a diagrammatic longitudinal section of the tube.

Figure 2 is a fragmentary detail showing a modified embodiment of thecathode screen.

Referring now more particularly to the drawing the reference character Egenerally designates the envelope of the present cathode-ray tube. Thisenvelope may be formed of glass, metal or other suitable material inaccordance with practice. This tube may be of any suitable design but ishere illustrated as of conventional design in having the relatively longstraight portion l0 having the closed end wall H and merging at itsother end in the flared or conical portion l2 which is closed by therounded front or convex wall l3. Upon the inner face of the wall I3 isapplied a coating or layer of a suitable fluorescent material 14.

In accordance with one embodiment of the present invention the rear endwall I I of the envelope is covered upon its inner side with a layer orcoating l5 of any suitable light sensitive mate rial such as, forexample, some alkaline metal like potassium or rubidium which emitselectrons when acted upon by light.

Suitably spaced from the electron emitting coating or electrode I5 isthe first anode l6 and disposed adjacent this anode but electricallyspaced therefrom, at the end of the anode nearest the cathode I5 is thegrid screen IT. This grid screen may be placed to encircle the end ofthe first anode nearest the cathode as illustrated but is, as previouslystated, in spaced relation therewith.

The first anode I6 is in the form of a tube or sleeve and encloses aseries of diaphragms l8 each of which has an opening l9 therethrough.These openings are aligned in a path oblique to the axial center of theanode for the purpose of condensing the electron stream entering fromthe cathode, to fiow out of the forward end of the first anode at anangle or oblique to the axial center of the envelope for the purposehereinafter stated.

Completing the electron gun is the second anode 20 which is located inthe customary manner in advance of the first anode and which is oftubular or sleeve like form and has within it the diaphragms 2| each ofwhich has a central opening 22 for the passage of the electron stream.The apertures 22 are aligned upon the axial center of the envelope andof the second anode so that the electron stream when flowing to thefluorescent screen without being acted upon by the deflection elements,will travel along the axial center of the envelope.

interposed between the first and second anodes is an electron multiplierunit which is indicated generally by the numeral 23. This unit 23 ismade up of a number, preferably four, of electrically separated plates25 which are of arcuate cross-section. These plates are assembled, asillustrated, to form a tube which is coaxial with the envelope and withthe first and second anodes.

The plates 23 of the electron multiplier unit 23 are of a metal having alow work function which when bombarded or struck by electrons moving athigh velocity, will emit electrons. The first electrode is constructedand arranged so that the electron stream passing therethrough will bedirected at an angle against the inner surfaces of the plate of themultiplier unit so as to create a secondary electron emission in thisunit. If such a unit were in the form of a single tube the electronsimpinging against the inner surface thereof and those electrons causedto be emitted .by such impingement would follow a sinusoidal path. Byforming such a tubular unit into sections as illustrated and by applyingelectric potential to the separate sections or plates, the electronswill, instead of describing one revolution, travel through manyrevolutions within the unit and by impingement a large number of timesagainst the inner surfaces of the plates before leaving the unit, causethe emission of large numbers of secondary electrons which will enterthe stream passing on from the multiplier unit to the second anode.

Any suitable means may be employed for applying potentials to the plates25 of the electron multiplier unit, one means being here shown as in theform of a number of series connected sources of potential 28 each ofwhich is connected by a pair of conductors 21 across two oppositelypositioned plates 23.

The inner surface of the envelope is covered by a suitable metalliccurrent conducting coating 28 which extends from a position adjacent tothe cathode I! to the opposite end of the envelope where it terminatesshort of the fluorescent screen II. This coating functions in thecustomary manner to drain off electrons from the fluorescent screen andis electrically connected with the grid screen ll in the arrangementshown when the grid screen is not employed to control the intensity ofthe electron stream under the action of the modulated current signalsreceived, when the tube is employed in receiving television signals.When this grid screen is made use of for controlling the intensity ofthe electron stream, the conducting coating 28 may be connected with thesecond anode is is customary, the grid screen ll then being hooked upwith thesignal receiving circuit to retard or accelerate the electronsemitted from the cathode. in response to signal variations.

The elements of the electron gun are here illustrated as being connectedwith a conventional voltage divider 23 whereby the desired potentialsmay be applied to the cathode, grid screen and anodes.

Deflection of the electron beam, designated B, to eifect the desiredmovement of the spot 23' may be accomplished by the employment of themagnet cells 30 or by the use of the well known deflection plates, notshown.

While there has been illustrated in association with the electronmultiplier unit 23, a cathode consisting of a light sensitive materialcoating at the inner end of the tube, the multiplier unit may beemployed, if desired, with a regular or standard hot filament cathodefor generating the electron stream or beam.

The invention also contemplates the employever since this formationfacilitates the focusing of the emitted electrons toward the center ofthe grid screen and into the adjacent end of the first anode.

The numeral 3| designates a light source for the production of a lightbeam 32 directed against the light sensitive electrode I! or 30'. Thislight beam 32 is preferably, though not necessarily, passed through acondensing lens 33, and then a polarizer 34 such as a Nicol prism, to asecond Nicol prism 35 which functions inthe well known manner as ananalyzer for the plane-polarized light beam issuing from the firstprism.

interposed between the prisms 34 and 33 is a light beam rotating unitwhich is indicated generally by the numeral 36 and by means of which theintensity of the light beam 32 can be diminished or caused to increaseto its maximum before striking the electron producing cathode in the endof the envelope. I

A second lens 31 may, if desired, be interposed between the analyzerprism and the cathode of the tube or envelope.

The light beam rotating unit 33. is of novel design in that it comprisesfour spaced parallel transversely arcuate plates 33 which are groupedabout and parallel the light beam, which beam passes along the center ofthe space between the grouped plates.

The plates of the light beam rotating unit are coupled as illustrated,through the medium of the transformer unit 33 with the signal receivingsy tem to receive the incoming signals. As a result the electrostaticfield between the plates 33 is constantly varied in intensity inaccordance with variations in the received signals. to thereby rotatethe plane-polarized light beam so that more or less thereof may passthrough the analyzer prism 35. The light beam density controlling unitor rotating unit 33 in effect consists of two Kerr In place of the lightbeam rotating unit 33 or Kerr type cell there may be used in thissystem, if desired, a supersonic light valve.

In the multiplier unit 23 a number of diilerent metals may be employedfor the production of the desired secondary emission of electrons. As anexample, there may be employed silver or platinum, silver having acoating of caesium or plati-' mim coated with caesiated silver, caesiumhaving a coating of caesium oxide, barium having a coating of bariumoxide, barium oxide on silver and silver plated platinum. In general,caesium coated metallic plastes or bodies will function as desired,using metals having a low work function. Rubidium having a coating ofrubidium oxide, or silver on platinum with a rubidium or other alkalimetal oxide may also be employed.

Metals having a low work function will produce the desired secondaryemission when stretched or placed under tension and such stretching ortensioning may be given to the above stated metals. Parkarized steelwith applications of the above stated metallic oxides may also beemployed.

It is to be understood that the envelope E of the present invention maybe filled or charged with a suitable gas which would aid in thedevelaccomplished with a lower current consumption and withoutsacrificing desirable features. With this improved cathode-ray tube alarger electron emission is obtained under low current voltage, with aconsiderably greater sensitivity, than is possible with tubes not havingprovision for secondary electron emission.

It will also be apparent that a new and novel arrangement is disclosedfor controlling the lumen intensity of the light pencil employed forexciting the light sensitive electron emitting substance upon the rearend of the tube.

Reference has been made to the use of Parkarized" steel as a suitablematerial to be used in the electron amplifier, either alone or as asupport for other electron emitting substances. This steel is prepared,broadly, by treating the metal, by dipping or in any other manner, withacids and then with alkalies which tends to make the surface of themetal somewhat rough and porous. Hence, the surface of such metal may bea good emitting surface under certain conditions.

I claim:

1. A cathode ray-tube including a source of primary electrons, a firstanode adjacent said source and a second anode, means for generatingsecondary electron emission comprising 2. cy' lindrical unit interposedbetween the first and second anodes and arranged to have the electronbeam from the [primary source directed therein to and against the innerwall thereof, said unit consisting of metal having the capacity to emitelectrons under electronic bombardment, said cylindrical unit beinglongitudinally divided to form a number of spaced parallel plates, andmeans for applying an electrical potential to said plates to set up anelectrostatic field therebetween.

2. In a cathode-ray tube, a primary source of electron emission at oneend of the tube, a first anode disposed in advance of said source, agrid screen adjacent said anode for directing the electron flow from thesource to the center of the first anode, a second anode spaced from thefirst anode, said first anode being constructed and arranged to focusthe electron stream toward the second anode along a path oblique to theaxial centers of the anodes, a tubular secondary electron emitting unitdisposed coaxially with and between the first and second anodes andspaced therefrom, the focusing anode functioning to direct the electronstream into and against the inner wall of said unit, and means forestablishing an electrostatic field within said unit.

3. In a. cathode-ray tube, a primary source of electron emission at oneend of the tube, a first anode disposed in advance of said source, agrid screen adjacent said anode for directing the electron fiow from thesource to the center of the first anode, a second anode spaced from thefirst anode, said first anode being constructed and arranged to focusthe electron stream toward the second anode along a, path oblique to theaxial centers of the anodes, a tubular secondary electron emitting unitdisposed coaxialiy with and between the first and second anodes andspaced therefrom, the focusing anode functioning to direct the electronstream into and against the inner wall of said unit, means forestablishing an electrostatic field within said unit, said source ofprimary electrons comprising a screen of light sensitive electronemitting material.

4. A cathode-ray tube structure as set forth in claim 2 in which saidsource of primary electrons comprises a screen of light sensitiveelectron emitting material, and means for applying a negative potentialto said screen and gradually increasing positive potentials respectivelyto the grid screen and first and second anodes.

5. A cathode-ray tube structure as set forth in claim 2 in which saidtubular unit comprises a series Of longitudinal spaced parallel platesdisposed in electrically separated relation, means for applying electricpotentials of opposite polarity to opposite plates of said unit, andmeans for applying a negative potential to said light sensitive screenand progressively positively increasing potentials respectively to thegrid screen and first and second anodes.

6. An electro-optical system comprising an evacuated tube having afluorescent screen at one end, a screen of light sensitive electronemitting material in the opposite end of the tube designed to emitelectrons under the action of light falling thereon, spaced first andsecond anodes within the tube and aligned between said screens, anelectron steam deflecting means, said second screen when subjected to alight beam emitting electrons, said anodes being arranged to receive andfocus said electrons onto the first screen, alight source disposed inposition to project a light beam on the second screen, a pair of Nicolprisms interposed between the light source and the second screen, andmeans interposed between the Nicol prisms for axially turning the lightbeam in response to changing electrical signal impulses to control theintensity of the light beam falling upon said second screen.

'7. A system as set forth in claim 6 in which said last means comprisestwo pairs of electrically separated plates disposed around and parallelwith the light beam and means for applying electric potentials ofopposite polarity to the opposite plates of each pair.

ROBERT EUGENE RIGHT-TS.

